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Background For Teachers:
Rocks can be broken down by physical or chemical weathering. Physical weathering is the cracking, breaking up, and grinding down of rocks into smaller pieces while maintaining the same mineral composition. This type of weathering is caused by a number of different factors. Changing temperatures cause rocks to crack and flake, ice splits rocks open, living things dig or pry open rocks, gravity causes rocks to fall and shatter, and abrasion breaks down rocks with solid particles like sand.
Chemical weathering is the breakdown of rocks as a result of a change in their mineral composition. In this type of weathering, minerals can either be added to or removed from rocks. Water and acids are the major destructive agents of chemical weathering because they can dissolve minerals that hold rocks together by chemically changing the rock and causing it to crumble. Acid rain, plant acids, carbonation, and oxidation can cause chemical weathering. Erosion, the transportation of weathered materials, and deposition, the deposit of these materials in a new location, are processes that often occur together. Erosion and deposition can be caused by various factors. Gravity pulls rocks down slopes, wind and running water pick up and carry loose materials, waves fragment the shoreline, and glaciers erode and carve away land as they move.
Weathering and erosion are two of the most important concepts in geology. They affect the landscape that we live on and are important in the formation of soil.
Over time, humans have learned techniques to minimize the effects of
these three forces of nature to preserve land formations and soil, which is
a valuable resource. Soil erosion can be slowed down by plant growth
covering bare soil. This is accomplished in two ways: 1) the roots hold
the soil in place, and 2) the vegetation absorbs the impact of the water
hitting the ground, lowering the velocity with which the water enters the
Intended Learning Outcomes:
Invitation to Learn
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